1. Field of the Invention
The present invention relates to a method of manufacturing a curved metal plate made of titanium or titanium alloy, and a golf club head using a plate of metal such as titanium alloy with ribs formed thereon manufactured by the press-bending technique.
2. Discussion of the Background
Titanium alloys have been hitherto used as materials for airplane and automobile parts, medical instruments, etc., because they exhibit high strength in spite of their relatively small specific gravity. In recent years, those titanium alloys are broadly used for such as golf, bicycle and other sporting and leisure equipment. Specifically, a cast product using Ti-6Al-4V is used particularly for fabricating a golf club head, because it better fits to a complicated shape of the golf club head. However, this product poses a problem of increasing the manufacturing cost and weakening the strength of the golf club head.
As a different approach to producing a desirable material for the golf club head, a metal plate made of SP700 having a hot workability or Ti-15V-3Al-3Cr-3Sn having a cold workability is plastically deformed to form a product for use in the golf club head.
Japanese Patent Publication No. 2640415 discloses one example of methods of manufacturing a driver head of the golf club. The method includes cold- or hot-pressing metal plates made of titanium alloy comprised of 10-25 wt. % of vanadium, and one or at least two metals selected from 2-5 wt. % of aluminum, 2-5 wt. % of chrome and 2-4 wt. % of tin into predetermined shapes, thereby forming parts of the driver head. Parts obtained in this manner are welded together to fabricate a driver head.
The above method using the titanium alloy as disclosed in the aforesaid Japanese patent publication requires such a large load as to plastically deform a titanium alloy or other plate material into a complicated shape of a golf club head or any other products. In addition, even if the metal plate made of titanium or titanium alloy has been press bent, it may be returned to nearly an original shape because titanium or titanium alloy has a substantial springback force. As a result, the manufacturing of a curved metal plate by the plastically deforming process involves a great difficulty.
In consideration of the above problem, it is an object of the present invention to provide a method of manufacturing a desirably curved metal plate even with a relatively small pressure load.
It is another object of the present invention to provide a golf club head with an excellent strength characteristics that can be securely manufactured by a press working.
Although even the conventional manufacturing method can achieve the reduction of the pressure load by reducing a contacting surface of a die to a workpiece, it would be hard to plastically deform the entire portion of the metal plate merely by reducing the die in size.
The present inventors studied and found that the contact surface of the metal plate to the die can be reduced by forming a recess such as in the form of a groove or hole on a die for press-bending a metal plate, and such a reduction results in a substantial reduction of the load regardless of the size of the die and hence a smaller springback force. The present inventors thus have achieved the present invention.
Specifically, a method of manufacturing a curved metal plate includes pressing a metal plate made of a plate material selected from titanium or titanium alloy with a die segment that forms thereon a convex surface curving in at least one direction and at least one recess, with a first side of the metal plate in contact with the convex surface, thereby curving the metal plate along the convex surface while allowing a part of the plate material on the first side of the metal plate to intrude into the at least one recess under pressure, thus forming at least one rib on the first side of the metal plate.
In the above method, the metal plate in contact with the convex surface of the die with the recess formed thereon is pressed by the die. Because the plate material intrudes into the recess under pressure, the recess can facilitate the flowing of the plate material during the press-bending operation. Furthermore, the recess is designed so that the plate material is prevented from filling in the recess. As a result, the contacting surface of the die and the workpiece is reduced, thereby achieving the reduction of the pressure load.
Because the plate material intrudes into the recess, the plate material on the first side contacting the recess is held by the recess, while increasing its tension force on a second side of the metal plate opposite to the first side. As a result, it is possible to restrain the curved metal plate to return to its original shape due to the springback force.
The recess may be formed in a groove, elongated groove or any other shape, of which the groove shape having at least a portion crossing the at least one direction along which the convex surface is curved is preferable. A plurality of recesses may be formed on the convex surface of the die. In such an arrangement, at least one of the plurality of recesses is preferably formed in a groove shape that has at least a portion crossing the at least one direction along which the convex surface is curved.
According to these preferred embodiments, during the press working of the metal plate, the plate material on the first side or the inwardly curving side converging in the direction along which the metal plate is curved securely intrudes into the recess or groove which has at least a portion crossing the direction along which the metal plate is curved. As a result, it can produce the aforesaid desirable effects that the metal plate is securely curved even with a relatively small pressure load, while more securely limiting the springback force.
Titanium or titanium alloy constituting the metal plate does not necessarily have a specific composition. However, beta-titanium alloy is preferable from the view point of the strength and any other properties. Particularly, titanium alloy having the following composition (wt. %): vanadium 15-25, aluminium 2.5-5, and tin 0.5-4 is more preferable.
The curved metal plate manufactured by the above method eventually forms thereon at least one rib or protrusion by the plate material intruding into the recess. The rib enhances the strength of the curved metal plate against an impact applied on the surface of the metal plate in the vertical direction, thereby reinforcing the curved metal plate.
Accordingly, a golf club head having at least a part formed from the curved metal plate manufactured by the present method has an excellent strength due to not only a material superiority of the titanium or titanium alloy, but also the shape of the metal plate.
Particularly, a beta-titanium alloy having the following composition (wt. %): vanadium 15-25, aluminium 2.5-5, tin 0.5-4, and titanium and unavoidable impurities constitute the residue is preferable when it is used for a golf club head, because it possesses a property achieving a higher strength after aging.